I love that the MTF have to sit in a shed."however the strangest part of SCP-XXXX-1, is that it will seem to negate all physical matter" I'd say that you should remove the word "strangest" be more absolute, I don't need to know its strange, Ill make that assumption myself.

I've also noticed a grey area in regards to the SCP's abilities and testing procedures the containment instrctions. Because it appears at complete randomness do the Foundation just sit in the testing chamber and hope to catch an apperance for the test? If not does the SCP broadcast long enough for them to prepare for the experiment and see it through? Specifying broadcast length would be a plus.

Lastly how are infected XXXX-3 instances spreading the "tunes", do they emit it themselves? Do they coax friends and family to listen to the radio? And do they still attempt to spread the "tunes" when there is no broadcast happening?

Lets start with a few noticeable grammatical errors. You have a major issue with misusing commas and creating run on sentences. For example, in the containment procedures we have this sentence.

"Should any manifestation of SCP-XXXX-1 be allowed to broadcast freely, all radio communications and broadcasting stations in the ████████, █████ and ███████ ████ regions are to be immediately deactivated and all recordings are to be destroyed, unless overruled by at least two(2) level four(4) personnel."

This can be easily be broken down into two sentences.

"Should any manifestation of SCP-XXXX-1 be allowed to broadcast freely, all radio communications and broadcasting stations in the ████████, █████ and ███████ ████ regions are to be immediately deactivated. All recordings are to be destroyed, unless overruled by at least two(2) level four(4) personnel."

Here is a much worse example from the description.

"Upon entering the structure, SCP-XXXX-1 will move directly towards SCP-XXXX, however the strangest part of SCP-XXXX-1, is that it will seem to negate all physical matter, with the exception of SCP-XXXX, making it physically impossible to intercept SCP-XXXX-1."

Here I broke the run on into three separate sentences.

"Upon entering the structure, SCP-XXXX-1 will move directly towards SCP-XXXX. However, the strangest part of SCP-XXXX-1 is that it will seem to negate all physical matter, except for SCP-XXXX. It is physically impossible to intercept SCP-XXXX-1."

You really need to go back and work on how to correctly use commas in your writing. The article is teeming with extra commas. You really need to break down those overly long sentences into multiple smaller ones. Variation in sentence length keeps your reader from getting bored.